Alkylation aide for sulfuric acid catalyzed alkylation units

ABSTRACT

The efficiency of acid catalyzed alkylation of alkanes with olefins is improved by conducting the alkylation in the presence of small amounts of a fatty acid having 16 to 40 carbon atoms.

FIELD OF THE INVENTION

This invention relates to a process for alkylating hydrocarbons and moreparticularly to a more improved process of alkylating aliphatichydrocarbons, particularly branched-chain aliphatic hydrocarbons witholefinic hydrocarbons in the presence of a strong acid.

BACKGROUND

The value of hydrocarbons can often be enhanced by alkylation of lowerhydrocarbons to produce higher molecular weight hydrocarbons. Forexample, isobutanes can be alkylated with isobutene to produce isooctanewhich is valuable for increasing the octane rating of gasoline. A commoncommercial method for alkylating a hydrocarbon is to react thehydrocarbon with selected olefins in the presence of a strong acid suchas sulfuric acid. Unfortunately, such acid solutions are not readilymiscible with organic liquids. Consequently, in alkylation processescatalyzed by strong acids, it has been necessary to use considerableexcess acid to effect a commercially feasible degree of alkylation. Theunused acid is discarded with the spent acid thereby reducing theefficiency of the process and augmenting the already burdensome wastedisposal problem. Improvements which will reduce the amount of acidwaste have long been sought.

PRIOR ART

In attempts to improve the efficiency of acid catalyzed alkylationsreaction temperatures have been lowered, the mixing efficiency has beenincreased and the ratio of hydrocarbon to olefin has been varied. Noneof these techniques has meet with significant success.

Chemical approaches have also been attempted. For example, variouschemicals have been added to acid-catalyzed alkylation reaction mixturesto promote more efficient use of the acid catalyst. Thus, U.S. Pat. No.3,324,196, issued to Kramer et al, discloses the use of an amine oramide containing at least one C₈ to C₂₀ aliphatic group to promote theacid-catalyzed alkylation of aliphatic and aromatic hydrocarbons. U.S.Pat. No. 2,880,255 discloses the use of mercaptans or combinations ofaliphatic amines and mercaptans to promote the alkylation ofhydrocarbons.

U.S. Pat. No. 3,778,489 discloses the use of carboxylic acids having 1to 10 carbon atoms as promoters for the sulfuric acid-catalyzedalkylation of a paraffin with a combination of olefins. U.S. Pat. No.3,766,293 discloses the use of carboxylic acids having 2 to 10 carbonatoms as promoters for the flurosulfuric acid-catalyzed alkylation of aparaffin with an olefin. U.S. Pat. No. 2,286,184 discloses the use oflow molecular weight mono-carboxylic and dicarboxylic acids as modifiersfor the sulfuric acid catalyzed alkylation of isoparaffins and olefins.

The present invention is based on the use of chemical additives topromote alkylation reactions. It has been discovered that certainorganic acids increase the efficiency of acid-catalyzed alkylationreactions. Accordingly, it is an object of the invention to present animproved alkylation process. It is another object of the invention topresent an improved process for alkylating hydrocarbons with acidcatalyst. It is another object of the invention to reduce the acidconsumption in acid-catalyzed alkylation reactions. These and otherobjects of the invention are supported in the following description andexamples of the invention.

SUMMARY OF THE INVENTION

It has now been discovered that the highly efficient alkylation ofaliphatic hydrocarbons by means of strong acid catalysts can be effectedby carrying out the alkylation reaction in the presence of at least onefatty acid having about 16-40 or more carbon atoms.

DETAILED DESCRIPTION

Long chain fatty acids usable in the invention include aliphatic acids,other than neo acids, having about 16 to 40 or more carbon atoms.Although fatty acids having more than 40 carbon atoms can be used in theinvention, fatty acids having no more than 40 carbon atoms are preferredbecause they are more readily available and easier to handle. In thepreferred embodiment the aliphatic fatty acid has 16 to 36 carbon atomsand in the most preferred embodiment about 16 to 20 carbon atoms permolecule. The fatty acid may be saturated or ethylenically unsaturatedand may be linear or branch-chained. The preferred aliphatic fatty acidsare the unsaturated fatty acids. As can be appreciated mixtures of twoor more fatty acids can be used in the invention. In general, suitablefatty acids are those having the structural formula ##STR1## wherein Ris hydrogen or a saturated or ethylenically unsaturated, linear orbranch-chained hydrocarbon group and R' is a saturated or ethylenicallyunsaturated linear or branched-chained hydrocarbon group and the averagesum of the carbon atoms in R and R' is 14 to 38. Preferably the averagesum of the carbon atoms in R and R' is 14 to 34 and most preferably 14to 18.

Examples of suitable fatty acids include saturated fatty acids, such aspalmitic acid, stearic acid, arachidic acid, lignoceric acid, 2-methylpentadecanoic acid, 2-ethyl palmitic acid, etc. Suitable unsaturatedfatty acids include oleic acid, linoleic acid, palmitoleic acid,petroselenic acid, ericic acid, etc. Commercially available hydrolyzedfats and oils and bottoms products contain mixtures of the above fattyacids and these may be conveniently used in the invention. Examples ofsuch fat acids include tall oil fatty acid, palm oil fatty acid, peanutoil fatty acid and cotton seed oil fatty acid. Mixtures of two or moreof the above fatty acids and fat acids may also be used in theinvention. Preferred acids include stearic acid, oleic acid, linoleicacid and the fat acids such as tall oil fatty acid.

The carboxylic acid alkylation aide may be used in any acid-catalyzedalkylation reaction between hydrocarbons and olefins. Hydrocarbons whichare often alkylated include saturated aliphatic and cycloaliphatichydrocarbons and aromatic hydrocarbons. These alkylation aides areparticularly useful in the alkylation of lower branched-chain alkanes,such as isobutane and isopentane with lower olefins to produce octanerating improving additives for gasoline. Lower alkanes which aredesirably alkylated include those having 4 to 10 carbon atoms.

Olefins which are used in alkylation reactions include those monoolefinshaving 3 to 10 carbon atoms. The olefins may be straight- orbranched-chain and the olefinic unsaturation may be located anywhere inthe structure of the compound.

Particularly useful gasoline additives for increasing the octane ratingare the branched octanes such as the compounds or mixture of compoundsobtained when isobutane is alkylated with mixed butenes. Branchedoctanes can also be prepared by the reaction of other alkanes andolefins, for example by the reaction of isopentane and propylene.

Various strong acids are useful for catalyzing the alkylation ofaliphatic or aromatic hydrocarbons with an olefin. Sulfuric acid,because of its efficiency and low cost, is the most commonly used acidalkylation catalyst. Other strong acids which can be used includehydrofluoric acid, phosphoric acid and fluorosulfonic acid. Any of theother well known strong acids are also useful for catalyzing alkylationreactions. Strong Lewis acids, such as aluminum bromide, aluminumchloride, antimony pentafluoride, antimony pentachloride, borontrifluoride, etc., can also be used as the acid catalyst in the processof this invention. In general, the alkylation promoters of the inventioncan be used with any known acid alkylation catalyst.

The alkylation reaction is carried out with all of the reactants in theliquid phase. The temperature of the reaction is that generally used foralkylation reactions. Reaction temperatures can vary from below 0° to ashigh as or higher than 200° F. The pressure of the reaction is notcritical and any pressure which will maintain the reactantssubstantially in the liquid phase may be employed. Pressures generallyrange from atmospheric to as high as 100 psi or higher.

The amount of fatty acid promoter added to the reaction mixture usuallyvaries from about 0.0005 to 5.0 percent, based on the total weight ofcatalyzing acid present in the reaction mixture. Amounts less than0.0005 weight percent generally produce insignificant results andamounts greater than about 5.0 weight percent are generally unnecessary,although such higher concentrations can be used, if desired. Thepreferred fatty acid lower concentration is about 0.001 percent and themost preferred minimum level is about 0.0025 percent, based on the totalweight of acid catalyst in the reaction mixture. The preferred upperlimit of the fatty acid concentration is about 1.0 percent and the mostpreferred upper limit is about 0.5 percent, based on the total weight ofacid catalyst in the reaction mixture. The optimum amount of fatty acidwill, of course, vary depending upon the particular fatty acidsemployed, the particular strong acid catalyst used and the particularhydrocarbons and olefins being reacted.

The alkylation promoters of the invention may be used with otheradditives, if desired. For example, other alkylation promoters may beused in combination with the promoters of the invention or surfactantsor other agents may be added to the reaction mixture.

In a typical application of the invention the hydrocarbon to bealkylated such as a lower branched-chain alkane and an olefin areintroduced into a suitable alkylation reaction vessel at a controlledtemperature, usually in the range of about 40° to 60° F., and at apressure sufficiently high to maintain the reactants in the liquidstate. The ratio of alkylatable hydrocarbon to olefin alkylating agentis preferably maintained at a high ratio, e.g. about 10:1, to minimizethe amount of alkyl sulfate formed by the reaction of olefin withsulfuric acid. An acid alkylation catalyst, such as sulfuric acid, andthe fatty acid alkylation promoter are introduced into the reactor,preferably on a continuous basis. At the end of the desired reactionperiod the finished product is removed from the reaction vessel andseparated from the spent acid. The reaction may be carried out on eithera batch or continuous basis.

The invention is further illustrated in the following examples. Unlessindicated otherwise, parts and percentages are on a weight basis.

EXAMPLE

The efficiency of an alkylation reaction is dependent upon the contacttime between the alkylation catalyst and the hydrocarbon beingalkylated; the longer the contact time, the more efficient is thealkylation reaction. The alkylation aide increases thecatalyst-hydrocarbon contact time. This demonstrates the effectivenessof the alkylation aides of the invention. The test procedure is asfollows: Fifty ml of 98% H₂ SO₄ and 50 ml of iso-octane are introducedinto a 100 ml graduate cylinder having a ground glass stopper. In thecontrol run no alkylation additive is used and in the comparative runand the run illustrating the invention 500 ppm of alkylation aide isadded to the test mixture. The stoppered cylinder is mechanically shakenfor 60 seconds after additive introduction and the time required for theentrained H₂ SO₄ to separate from the hydrocarbon layer and the timerequired for the entrained hydrocarbon to separate from the H₂ SO₄ layerare measured. The results are tabulated in the table.

                  TABLE                                                           ______________________________________                                                            Separation Time (sec).                                    Run  Additive      Conc. (ppm)                                                                              Hydrocarbon                                                                            H.sub.2 SO.sub.4                       ______________________________________                                        1    None (Control)                                                                              --          2.38     7.12                                  2    Lauric Acid (C.sub.12)                                                                      500        24.02    48.94                                  3    Tall oil fatty acid.sup.1                                                                   500        39.48    69.20                                  ______________________________________                                         .sup.1 Sold by Westvaco Chemical Company under the trademark L5.         

As illustrated in the example, use of the alkylation aide of theinvention (Run 2) results in a significantly greater contact time inboth the hydrocarbon and H₂ SO₄ phases than when no alkylation aide isused.

Although the invention is described with particular reference tospecific examples it is understood that the invention includesvariations. For example, other hydrocarbons, such as aromatic compounds,may be alkylated or other olefins or acids may be used. The scope of theinvention is limited only by the breadth of the appended claims.

We claim:
 1. In an alkylation process comprising contacting analkylatable hydrocarbon with an olefinic alkylating agent at alkylationconditions in the presence of an acid catalyst and an alkylationpromoter, the improvement comprising using as the promoter a fatty acidhaving the structure ##STR2## wherein R is hydrogen or a saturated orethylenically unsaturated hydrocarbon radical and R' is a saturated orethylenically unsaturated hydrocarbon radical and the average sum ofcarbon atoms in R and R' is 14 to
 38. 2. The improved process of claim 1wherein the average total sum of carbon atoms in R and R' is 14 to 34.3. The improved process of claim 1 wherein said alkylatable hydrocarbonis an alkane and said olefinic alkylating agent is a monoolefin.
 4. Theimproved process of claim 3 wherein said alkane has 4 to 10 carbon atomsand said monoolefin has 3 to 10 carbon atoms.
 5. The improved process ofclaim 4 wherein said alkane is branch-chained.
 6. The improved processof any one of claims 3 to 5 wherein the concentration of alkylationpromoter present in the reaction zone is about 0.0005 to 5.0 percent,based on the total weight of acid catalyst present in the reaction zone.7. The improved process of any one of claims 3 to 5 wherein theconcentration of alkylation promoter present in the reaction zone isabout 0.001 to 1.0 percent, based on the total weight of acid catalystpresent in the reaction zone.
 8. The improved process of claim 6 whereinthe average total sum of carbon atoms in R and R' is 14 to
 18. 9. Theimproved process of claim 7 wherein the average total sum of carbonatoms in R and R' is 14 to
 18. 10. In an alkylation process comprisingcontacting a saturated aliphatic hydrocarbon having 4 to 10 carbon atomswith at least one olefinic alkylating agent having 3 to 10 carbon atomsat alkylation conditions in the presence of a strong acid catalystselected from sulfuric acid, phosphoric acid, hydrofluoric acid,fluorosulfonic acid and mixtures of these and an alkylation promoter,the improvement comprising using as the alkylation promoter about 0.001to 1.0 percent, based on the total weight of strong acid catalyst of acomponent comprised of at least one carboxylic acid having the structure##STR3## wherein R is hydrogen or a saturated or ethylenicallyunsaturated hydrocarbon group and R' is a saturated or ethylenicallyunsaturated hydrocarbon group and the average total sum of carbon atomsin R and R' is 14 to
 34. 11. The improved process of claim 10 whereinthe average total sum of carbon atoms in R and R' is 14 to
 22. 12. Theimproved process of claim 10 wherein said fatty acid is an unsaturatedfatty acid.
 13. The improved process of claim 1 wherein said fatty acidis selected from oleic acid, linoleic acid, tall oil fatty acid, palmoil fatty acid, peanut oil fatty acid, cotton oil fatty acid andmixtures of these.
 14. The improved process of any one of claims 10 to12 wherein the saturated aliphatic hydrocarbon is branch-chained. 15.The improved process of claim 14 wherein the alkylation promoter ispresent in an amount of about 0.0025 to 0.5 percent, based on the totalweight of strong acid catalyst present in the reaction zone.